Standardization means that the dairy processes the incoming whole milk, the fat content of which may vary, to make market milk with a specified constant fat content—standardized milk. If the specified constant fat content is higher than that of the incoming whole milk, the process will involve removing some of the skim milk, and the dairy will have a skim milk surplus. Normally, however, standardization proceeds to a lower fat content than that of the incoming whole milk. The process therefore leaves a surplus of fat, which can be used for example to make butter. The same type of standardization applies also for e.g. whey standardization, cream concentration, milk separation at high temperatures, where the milk is melted, or at lower temperatures, where the milk fat is solid or partly solid, or milk with ingredient addition.
The process of standardization can be arranged in three different ways: prestandardization, poststandardization, or direct standardization in line. The first step in all three methods is to separate whole milk into cream and skim milk.
Prestandardization means that the milk is standardized before being pasteurized. To adjust the fat content upward, separated cream is mixed with raw whole milk in tanks in proportions calculated to give the required fat content. To standardize to a lower fat content, the raw whole milk is diluted with separated skim milk. After analysis and adjustment, the standardized milk is pasteurized.
In poststandardization, pasteurized whole milk is mixed in tanks with either cream or skim milk, according to whether the fat content is to be adjusted upward or downward, in the same way as in the case of prestandardization. However, as poststandardization involves mixing already pasteurized products, some risk of reinfection is involved. Both methods, moreover, require the use of large, bulky tanks, and the work of analysis and adjustment is labour-intensive.
The third method, direct standardization, has therefore been an attractive alternative for industrial needs. In this method, the fat content is adjusted to the desired level by immediate remixing of a calculated proportion of the cream flow from the separator to the skim milk line.
Direct standardization begins with separation of cold or preheated whole milk into cream and skim milk of constant fat content. A regulated amount of cream is then remixed with the skim milk in an in-line system immediately after the separator to obtain standardized milk of the required fat content.
Some small amounts of bacteria and spores will unavoidably be present in the flow of raw milk. The low flow of bacteria and spore concentrate in conjunction with high flow of product through the separator leads to sensitivity to blockage due to bacteria and spore residues. To prevent this discharges are made at certain time intervals. When discharging the separator all products is discarded and the separator is reset to its initial state, free from residues of spores and bacteria. Each discharge of the separator, however, by its nature leads to product loss which is not desired. To ensure that the concentration of bacteria and spores in the end product is not too high the separator is discharged well before any risk of too high bacteria concentration in the product. However, the clogging of the separator is not linear and depends on the batch of the raw milk etc. Therefore, the time interval for discharge of the separator has to be set to the worst case scenario, leading to the situation that the separator in most cases is discharged long before it would have to.
There is thus a need of a better control system for discharging of separators in the dairy industry to reduce the amounts of discarded product and thereby reduce losses and costs in the dairy.